Well just to throw it out there, a doctors job is to be a pessimist. Just saying... I know quite a few, and that's what they tell me! lol!
On another note, no doctor can predict the future... just doesn't happen. They are making an educated guess to the best of their ability given the data and results they receive from tests and talking to you. They are doctors, not freaking psychics. To make a guess on something and tell you this in such a tight knit time frame of the age 30 - 31 and this on top of it being 14 years or so down the road is a bit far fetched. If a doctor or certified medical personnel member tells you a time frame, it's never that long. the LONGEST time frame I've ever seen given on a guess was 3 - 5 years, and that was on life expectancy, not something like hearing. Life expectancy yes, they'll try and time it based on a VITAL organ or whatever failing, but something as minor as hearing... a 14 year or so expectancy? I'm sorry, I just can't believe it. ( I'm a Paramedic so yes, I work with a LOT of doctors )
Most doctors would not tell you an age limit on when you were going to go deaf... I saw MANY doctors when I began losing my hearing, and while all of their opinions were similar and some different, not ONE single doctor told me a time frame, and wouldn't. They would say, "it could be tomorrow, it could be 10 years, it could be never, everyone is different..." which is true and I understood that.
To throw on top of the matter, I'd make sure you're not speaking to just "any old doctor" and speaking to an audiologist, ENT and possibly another kind of specialist. Someone who's just is specifically hearing... Doctors are for general stuff, they're usually not specialists unless you seek said specialist.
It sucks about tinnitus... it's a terrible thing to have, and yet pretty common. I recommend seeing a different doctor if this story is the truth... because this doctor you're seeing seems off his game, or just stupid... Whichever you prefer. Not trying to be mean, but it's either 1) your doctor needs to go back to medical school 2) your doctor needs some more training 3) This is not the case. So if this is your case, seek a medical professional, and someone who has experience in this...
Also as Bott said, lots of people have it and never go deaf or lose hearing... so why would something that so often never effects hearing have a time stamp of 14 years or so placed on it by a doctor? Makes absolutely no sense to me at all.
Again, my condolences to you and the tinnitus, it can be annoying, but it's not life ending... and there's a good chance it won't effect anything with your hearing.